Herbert Weir Smyth, A Greek Grammar for Colleges

STOPS BEFORE M

ὄμμα eye for ὀπ-μα (cp. ὄπωπα), λέλειμμαι I have been left for λελειπ-μαι from λείπ-ω leave, τέτρι_μμαι for τετρι_β-μαι from τρί_β-ω rub, γέγραμμαι for γεγραφμαι from γράφ-ω write, πέπλεγμαι for πεπλεκ-μαι from πλέκ-ω plait, τέτευγμαι for τετευχ-μαι from τεύχ-ω build.

a. κ and χ may remain unchanged before μ in a noun-suffix: ἀκ-μή edge, δραχ-μή drachma. κμ remains when brought together by phonetic change (128 a), as in κέ-κμη-κα am wearied (κάμ-νω).

[*] 85 a D. So in Hom. ἴκμενος favoring (ἱκά_νω), ἀκαχμένος sharpened.

b. γγμ and μμμ become γμ and μμ. Thus, ἐλήλεγμαι for ἐληλεγγ-μαι from ἐληλεγχ-μαι (ἐλέγχ-ω convict), πέπεμμαι for πεπεμμ-μαι from πεπεμπ-μαι (πέμπ-ω send).

[*] 86. A dental stop (τ, δ, θ) before μ often appears to become ς. Thus, ἤνυσμαι for ἠνυτ-μαι (ἀνύτ-ω complete), πέφρασμαι for πεφραδ-μαι (φράζω declare), πέπεισμαι for πεπειθ-μαι (πείθ-ω persuade).

[*] 87. On the other hand, since these stops are actually retained in many words, such as ἐρετμόν oar, πότμος fate, ἀριθμός number, ς must be explained as due to analogy. Thus, ἤνυσμαι, πέφρασμαι, πέπεισμαι have taken on the ending -σμαι by analogy to -σται where ς is in place (πέφρασται for πεφραδ-ται). So ἴσμεν we know (Hom. ἴδμεν) follows ἴστε you know (for ἰδ-τε). ὀσμή odor stands for ὀδ-σμη.