A genuine demonstration or appearance of a quality, emotion, etc. Also as a mass noun. Without such modifiers.

figurative. An outgoing of emotion. Obsolete.

figurative. A pouring forth, unrestrained utterance (of words, sounds, etc.); frank and eager expression (of emotions).

figurative. An outburst (of feeling); a sally (of wit); an overstepping of the bounds of propriety or custom, a freak; vagary, escapade. Obsolete.

A breaking forth from restraint; an outburst or transport (of passion, delight, or other emotion); a flash (of wit); a flight (of fancy).

Open and unreserved expression of feelings, esp. affection; effusiveness. (Now the usual sense.)

colloquial. Extravagant display of feeling or sentiment.

figurative. Outflow (of affection, etc.).

As a mass noun: outward exhibition of feeling; demonstrative behaviour.

the quality of being effusive.

Violent or copious outflow; effusiveness.