A hendiad is a phrase is created through hendiadys: a noun and its modifier (an adjective) is replaced by two nouns connected by a conjunction (usually and). It is a stylistic or rhetorical device that adds emphasis and force, as in "she braved the rain and weather" rather than "she braved the rainy weather", or "grace and favour" instead of "gracious favour". It's derived from the Greek hen (one), dia (through), and dys (two), so "one by means of two".

Hendiadys is a subset of anthimeria, the substitution of one part of speech for another (normally in English a noun used as a verb).

humanities.byu.edu/rhetoric/Figures/H/hendiadys.htm
www.brown.edu/Departments/English/curriculum/el31/rhetfig/hendiad.html