"Love me tender": adverb or adjective?
We can know because grammar books define the parts of speech. An adverb (among other things) modifies a verb, expressing manner (e.g., gently). Adjectives modify nouns. In Love Me Tender, what is the subject, verb, direct object, and then what does that left-over word modify? Here's my take:
Love me tender: subject (implied): you; verb: love; direct object: me; left over word - does it modify you, me, or love?
Tender-you love me. (meh) You love tender-me. (good reason for loving me, but I don't think so.) You tender-love me. (sounds good to me! We usually say tenderly.)
Love me tender(ly)
love me sweet(ly),
never let me go.
You have made my life complete,
and I love you so.
Love me tender(ly),
love me true(ly),
all my dreams fulfilled.
For my darlin' I love you,
and I always will.
Love me tender(ly),
love me long(ok, you decide),
take me to your heart.
For it's there that I belong,
and we'll never part.
Love me tender(ly),
love me dear(ly),
tell me you are mine.
I'll be yours through all the years,
till the end of time.
Because young Elvis.
It is an adverb because it should read:
"Love me tenderly, love me slowly."
Tenderly and slowly are both describing the verb love.
Moden English usage frequently uses an adjectival form where there should correctly be an adverbial form. How many times have you heard this: He drove real slow.
If you want to hear grammatically correct lyrics, you should really listen to Sir Cliff.
It is a typical characteristic of colloqial AmE ( American English) to use the adjective form after a verb instead of the adverb with the ending -ly. And the probability is high that this use is due to German influence. In German normal adjectives after a verb have the function of an adverb; there is no special adverb ending. The position after a verb clearly indicates the function of an adjective as adverb. BrE He speaks beautifully. AmE He speaks beautiful. (colloquial style) German Er spricht schön.
Based on the rest of the lyric, where "nice" and "tight" are both adverbs, "tender" should also be an adverb.