Why is 'hyper-' considered a prefix, but 'tachy-' is considered a combining form?

Solution 1:

There isn't really any clear definition of "prefix". However, in general, elements of complex words that are derived from nouns or adjectives are not called prefixes. E.g. the black in the English word blackbird is not considered to be a prefix.

Tachy- is from the the Greek adjective ταχύς.

Hyper- is from the Greek preposition/adverb ὑπέρ. It's fairly common for Greek or Latin prefixes to come from prepositions or adverbs.

Solution 2:

"Tachy" (from ancient Greek) means "fast" as in tachycardia, tachypnea, tachygraphy, meaning fast heart rate, fast breathing and fast writing, respectively.

prefixes are defined as "morphemes (specific groups of letters with particular semantic meaning) that are added onto the beginning of roots and base words to change their meaning. Prefixes are one of the two predominant kinds of affixes—the other kind is suffixes, which come at the end of a root word."

In medicine, both tahchy- prefix and its opposite, brady- prefix, are considered prefixes, so I was taught in Medical School.

Based on the definition of "prefix", I would say "tachy-" is a prefix and The Free Dictionary backs me up, as well as The UCL and several other sources. Whilst "tachy" is a prefix, "tachycardia" is a compound word. DC