Rhema has a broad definition:The first time Rhema is used in the New Testament is during Jesus' forty-day temptation by Satan.
Strong's Concordance
rhéma: a word, by impl. a matter
Original Word: ῥῆμα, ατος, τό
Part of Speech: Noun, Neuter
Transliteration: rhéma
Phonetic Spelling: (hray'-mah)
Definition: a word, by implication a matter
Usage: a thing spoken, (a) a word or saying of any kind, as command, report, promise, (b) a thing, matter, business.
Thayer's Greek Lexicon
STRONGS NT 4487: ῤῆμα
...properly, that which is or has been uttered by the living voice, thing spoken, word
....any sound produced by the voice and having a definite meaning
...the word by which something is commanded, directed, enjoined
...speech, discourse
...words, sayings
...an utterance, declaration