In a previous daf, Gittin 65b, we see a strange phrase, מֵיגָס גָּאֵיס, which appears only once in the Talmudic corpus.
לָא צְרִיכָא, דַּאֲמַרָה לֵיהּ: ״זִיל לְמִזְרָח, דְּאִיתֵיהּ בְּמִזְרָח״; וְקָא אָזֵל לְמַעֲרָב. מַהוּ דְּתֵימָא, בְּמַעֲרָב – הָא לֵיתֵיהּ; קָא מַשְׁמַע לַן, דִּילְמָא בַּהֲדֵי דְּקָאָזֵיל מֵיגָס גָּאֵיס בֵּיהּ, וִיהַב לֵיהּ גִּיטָּא.
The Gemara answers: No, Rabbi Elazar’s ruling is necessary in a case where she said to him: Go to the east, as my husband is in the east, and the agent went to the west. Lest you say that since the husband is certainly not in the west and the agent will not find him there, the bill of divorce will certainly not take effect until later, Rabbi Elazar teaches us that perhaps while he was going west, the agent happened to encounter the husband, and the husband gave the bill of divorce to the agent.
Jastrow provides a definition, first noting the Hebrew and then the Chaldean (Aramaic) cognate. He mentions a parallel in Pesachim, so that it means to meet, to encounter:
Rashi on the daf also gives a handy definition, namely:
מיגס גייס ביה - פוגע בו:
A definition works by substituting a more common, well-known word, for the lesser-known, rare word.
Interestingly, there are manuscripts which have pogea. Namely, Munich 95 and Vatican 130 have מיפגע קפגע or ומיפגע פגע.
However, I think it is clear that these were later reworkings of the text. Perhaps as a deliberate rewriting to make the text more understandable, or as something marginal that entered the main body of text. The principle of lectio difficilior, the law that the more difficult reading is original, pertains here.