Physiology . a period of decrease of reproductive capacity in men and women, culminating, in women, in the menopause.

any critical period.

a year in which important changes in health, fortune, etc., are held by some theories to occur, as one's sixty-third year (grand climacteric).

the period of maximum respiration in a fruit, during which it becomes fully ripened.

Also, climacterical

noun

crossroad , exigence , exigency , head , juncture , pass , turning point , zero hour

adjective

acute , crucial , desperate , dire