What is the definition of "iat" in Commissariat/Secretariat

What is the definition of "iat" in Commissariat/Secretariat, also what are some other "iat" words. (Links, if you have any, please.)

Solution 1:

The -i- just happens to be there because it is part of the words they were derived from, i.e. secretarius and commissarius. The ending -at(e) describes either 1) an office, function, or abstract entity related to the word it is derived from, or 2) a passive participial noun, such as mandate "something that is demanded". The ending -at is simply a spelling variation of -ate.

In Latin, the regular past participle of verbs is made by adding the suffix -t- to the stem plus the ending -us/-a/-um (1st/2nd declension). So English minute is from minu-t-us "diminished", from minuo "to diminish, to make small": a very small piece cut off from an hour. (Note that diminish is from the related Latin di-minuo.)

Words denoting an abstract entity, such as an action or an office, can be made by adding -us (4th declension) to the stem on -t-. So English advent is derived from adven-t-us, "the act or process of arriving", from advenio "to arrive".

When you want to form a past participle based on something that isn't a verb, you often add -a- in between. Based on that, magister "master" led to magistr-a-t-us (2nd declension) "someone made into a master, a magistrate", or (4th declension) "the office of being a master, the magistrature". Both words could legitimate be formed based on magister. This was also done with secretari-us (regular adjective) => secretari-atus (4th declension, abstract entity)¹ and commissari-us.

In French, both endings evolved into the ending -(a)t, from which English took secretariat, commissariat, proletariat, but also most of our other words on -ate and -it(e), which were mostly spelled without the -e until ca. 1400 in English, so says the Oxford English Dictionary. By that time, -e began to be regularly added to both kinds of words to mark the long vowel, but a few words kept their original French -at in English.

Verbs on -(a)te are also derived from the past-participial stem.

1) Purified Google search for a form of the 4th declension of secretariatus: plenty of hits. Purified Google search for a form of the 2th declension of secretariatus: only one hit, and that written in the 20th century. So Secretariat most probably comes from an abstract noun of the 4th declension.

Solution 2:

It’s basically a mixture of various endings.

In Latin, there are a group of adjectives that are derived with the suffix -ārius; some of these include:

sēcrētārius (‘having to do with a sēcrētum [secret]’)
commissārius (‘having to do with being commissus [in charge/committed]’)
prōlētārius (‘having to do with prōlēs [offspring, progeny]’

So the -ārius suffix means something like ‘having to do with X’.

These words were all originally adjectives, but for some reason, words with this particular suffix were particularly prone to be used as nouns. Sēcretārius, for example, meant something like ‘secretive’ or ‘confidential’, but went on to become used almost exclusively as a noun denoting a person who was these things: a secretary (or confidant).

Once this was the situation, there naturally arose a need to create an adjective corresponding to these nouns. The choice for a suffix to do this seems to have (somewhat oddly, perhaps) fallen on an analogical use of the suffix -ātus, which is really the passive participle suffix for first-declension verbs (āmō ‘I love’ -> āmātus ‘[be]loved’).

Why the late Romans chose this particular suffix is quite obscure—its meaning of ‘having been X-ed’ does not really fit with an adjective that just means ‘having to do with X’, after all … but choose it they did:

sēcrētārius -> sēcrētāriātus ‘having to do with someone who has to do with secrets’
commissārius -> commissāriātus ‘having to do with someone who has to do with having been put in charge’ (!)
prōlētārius -> prōlētāriātus ‘having to do with someone who has to do with offspring’

These might seem like quite roundabout ways to say things, but this kind of ‘recursive derivation’ is quite common in Latin. I don’t think the Romans really thought about them in that way; they probably just thought of sēcrētārius as a simplex word from which an adjective was derived.

As happened to their ‘parent’ words, the adjectives in -(āri)ātus in their turn also started to be used as nouns. Since the nominalised forms of -ārius adjectives often denoted people, the nominalised forms of the -(āri)ātus adjectives naturally tended to describe either places or groups that were connected to these people.

Since then, the words passed into French and lost their final syllables (and some vowel fronting and other historical magic took place to turn -ārius into -aire in Modern French and -ary in Modern English), and voilà: you have words with -ary and derived words in -ariat in English.