(BELOW STANDARD) [adjective] -er, -est - below standard; not good enough, esp. in ability, skill or qualityHe was always weak at/in languages but strong at/in science.Our quiz team is a bit weak on sport.In the end I think the film was spoilt by a weak story line.
WEAK
Meaning of WEAK in English
Cambridge English vocab. Кембриджский английский словарь. 2012