the.com/endearment

means A word or gesture that expresses affection, often a tender nickname like 'sweetheart' or 'love'.

from Traces back to the verb 'endear,' built from the prefix 'en-' (to make, to put into a state) plus 'dear.' 'Dear' itself descends from Old English 'deore,' meaning precious or costly — the same root that gives us the idea of something valued highly. So to 'endear' was literally to make someone precious to you, and an 'endearment' is the little verbal proof of that — a word that puts someone, however briefly, into the category of things you'd pay dearly for.