the adjective is long – the noun, length – the antonym, short. Lengthy is an often-used adjective and adverb meaning “quite long” or “very long” or even “tediously long.” It’s a little more descriptive than “long” and takes up 2 syllables rather than one.
In what contexts? written information, meetings, events. All taking longer than we’d like them to … and in any case … time-consuming! Here are just a few recent examples:
lengthy information sessions
a lengthy, secret memo
a lengthy criminal investigation
in a lengthy report
Actually a good contrary would be … “brief!”