before vowels path-, word-forming element in science and technical terms meaning "suffering, disease," from Greek pathos "suffering, disease" (from PIE root *kwent(h)- "to suffer").
word-forming element meaning "of or pertaining to medical science; from a medical standpoint; pertaining to medicine and," used as a combining form of Latin medicus "physician; healing" (from PIE root *med- "take appropriate measures").
word-forming element used in science and meaning "small, little," from combining form of Latin parvus "small," which is from a metathesized form of PIE *pau-ro-, suffixed form of root *pau- (1) "few, little."
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 indicating "branch of knowledge, science," now the usual form of -logy. Originally used c. 1800 in nonce formations (commonsensology, etc.), it gained legitimacy by influence of the proper formation in geology, mythology, etc., where the -o- is a stem vowel in the previous element.
The second element is prop[erly] -logy (-logue, etc.), the -o- belonging to the preceding element; but the accent makes the apparent element in E[nglish] to be -ology, which is hence often used as an independent word. [Century Dictionary]
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.
often before vowels pseud-, word-forming element meaning "false; feigned; erroneous; in appearance only; resembling," from Greek pseudo-, combining form of pseudēs "false, lying; falsely; deceived," or pseudos "falsehood, untruth, a lie," both from pseudein "to tell a lie; be wrong, break (an oath)," also, in Attic, "to deceive, cheat, be false," but often regardless of intention, a word of uncertain origin. Words in Slavic and Armenian have been compared; by some scholars the Greek word is connected with *psu- "wind" (= "nonsense, idle talk"); Beekes suggests Pre-Greek origin.
Productive in compound formation in ancient Greek (such as pseudodidaskalos "false teacher," pseudokyon "a sham cynic," pseudologia "a false speech," pseudoparthenos "pretended virgin"), it began to be used with native words in later Middle English with a sense of "false, hypocritical" (pseudoclerk "deceitful clerk;" pseudocrist "false apostle;" pseudoprest "heretical priest;" pseudoprophete; pseudofrere) and has been productive since then; the list of words in it in the OED print edition runs to 13 pages. In science, indicating something deceptive in appearance or function.