slow burn

Short definition from Wiktionary

Noun

1. 1
   Something that emerges or unfolds slowly or gradually.
2. 2
   Something that emerges or unfolds slowly or gradually: A gradually increasing expression of emotion, espeically anger or frustration.
3. 3
   Something that emerges or unfolds slowly or gradually: A work of fiction with a slow-paced plot; also, such a storyline.
4. 4
   A work of fiction with a slow-paced plot; also, such a storyline: A romantic story (especially a work of fan fiction) in which the central relationship develops slowly.
5. 5
   Alternative form of slow burn.

Adjective

1. 1
   Alternative form of slow-burn.
2. 2
   Emerging or unfolding slowly or gradually.
3. 3
   Emerging or unfolding slowly or gradually: Developing slowly over the course of the story.

Verb

1. 1
   To emerge or unfold slowly.