Adolescents - adolescence - adolescency
Adolescence and adolescents are both pronounced with the stress on the third syllable and sound the same, except in the most careful speech (IPA: /,æ də 'lɛ səns/. Both (and their related forms) are derived from the same root, the Latin adolescere - the verb of which the past participle, adultus, has given us the English word adult. The verbal suffix -escere (giving the adjective form -escent) means 'growing', 'becoming'; 'altering its state towards'.
- Adolescent can be either an adjective or a noun, as also can adult.
- The adjective adolescent means 'growing up'. It is used in English to refer specifically to the time between the beginning of puberty and full adulthood. It can be used to mean 'immature', as in a reprimand to a teenager behaving childishly, or a [young] adult forgetting his dignity: "that's so adolescent - you should be ashamed of yourself."
- The noun 'an adolescent' means a person of that age. Colloquially, a term often used is 'teenager'. When there is more than one, they are adolescents (or teenagers).
- Adolescence is the general state of being through which boys and girls must pass on their way to being men and women.
- The rarer - but useful - adolescency is defined by OED as "The quality or state of being adolescent, or in the growing age. Properly distinguished from ADOLESCENCE, as youthfulness is from youth, as in 'a protracted adolescence,' but 'evidences of adolescency'" (AWE's underlining).
AWE has a Table collecting some of the words that fall into a pattern of potentisl auditory confusion between '-ence' and '-nts'.