Leviticus 20:18

הערה means HE HATH UNCOVERED. Similarly the term ערוה everywhere denotes "uncovering". The ו in the word ערוה nakedness, is inserted in the root ערה in order to form a noun of it, just as the noun זעוה, "trembling", is of the same derivation as זע in the phrase (Esther 5:9) "and he stood not up and did not tremble (זע)". Similarly, אחוה "brotherhood", is of the same derivation as אח, brother. As for this term "uncovering" our Rabbis differ in the meaning they give to it (Yevamot 55b). Some say that it is the mere contact of the tip of the organ, while others say that it is the insertion of the tip.

וְ֠אִ֠ישׁ אֲשֶׁר־יִשְׁכַּ֨ב אֶת־אִשָּׁ֜ה דָּוָ֗ה וְגִלָּ֤ה אֶת־עֶרְוָתָהּ֙ אֶת־מְקֹרָ֣הּ הֶֽעֱרָ֔ה וְהִ֕וא גִּלְּתָ֖ה אֶת־מְק֣וֹר דָּמֶ֑יהָ וְנִכְרְת֥וּ שְׁנֵיהֶ֖ם מִקֶּ֥רֶב עַמָּֽם׃

And if a man shall lie with a woman during her menstrual sickness, and shall uncover her nakedness; he has made naked her fountain, and she has uncovered the fountain of her blood: and both of them shall be cut off from among their people.