1.
to give a cry, etc. :
to let out a scream of terror
to let out a gasp of delight
OPP hold in
2.
to make a shirt, coat, etc. looser or larger
OPP take in
LET STH OUT
Meaning of LET STH OUT in English
Oxford Advanced Learner's English Dictionary. Оксфордский английский словарь для изучающик язык на продвинутом уровне. 2005