word-forming element in modern science meaning "seaweed, algae," from Latinized form of Greek phykos "seaweed, sea wrack," also "rouge, red make-up made from seaweed;" Beekes writes that it is a loan-word from Semitic and compares Hebrew pūk "eye-rouge." "The meaning 'make-up' is therefore primary for [phykos], too; hence 'seaweed'." Compare fucus, which is probably a Latin borrowing of the Greek word.
word-forming element meaning "a speaking, discourse, treatise, doctrine, theory, science," from Greek -logia (often via French -logie or Medieval Latin -logia), from -log-, combining form of legein "to speak, tell;" thus, "the character or deportment of one who speaks or treats of (a certain subject);" from PIE root *leg- (1) "to collect, gather," with derivatives meaning "to speak (to 'pick out words')." Often via Medieval Latin -logia, French -logie. In philology "love of learning; love of words or discourse," apology, doxology, analogy, trilogy, etc., Greek logos "word, speech, statement, discourse" is directly concerned.
<a href="https://www.etymonline.com/word/phycology">Etymology of phycology by etymonline</a>
Harper, D. (n.d.). Etymology of phycology. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/phycology