מצחק "Miztachek," A Bit More Than "Sporting"

I'm referring to the verb מְצַחֵק as conjugated in Toldot when Rivka and Yitzchak are "spied" doing something that makes Avimelech think they must be married, not siblings.

ז וַיִּשְׁאֲלוּ אַנְשֵׁי הַמָּקוֹם, לְאִשְׁתּוֹ, וַיֹּאמֶר, אֲחֹתִי הִוא: כִּי יָרֵא, לֵאמֹר אִשְׁתִּי, פֶּן-יַהַרְגֻנִי אַנְשֵׁי הַמָּקוֹם עַל-רִבְקָה, כִּי-טוֹבַת מַרְאֶה הִוא.
7 And the men of the place asked him of his wife; and he said: 'She is my sister'; for he feared to say: 'My wife'; 'lest the men of the place should kill me for Rebekah, because she is fair to look upon.'
ח וַיְהִי, כִּי אָרְכוּ-לוֹ שָׁם הַיָּמִים, וַיַּשְׁקֵף אֲבִימֶלֶךְ מֶלֶךְ פְּלִשְׁתִּים, בְּעַד הַחַלּוֹן; וַיַּרְא, וְהִנֵּה יִצְחָק מְצַחֵק, אֵת, רִבְקָה אִשְׁתּוֹ.
8 And it came to pass, when he had been there a long time, that Abimelech king of the Philistines looked out at a window, and saw, and, behold, Isaac was sporting with Rebekah his wife.

Here מְצַחֵק is translated as "sporting."

We've had that word before, telling that Ishmael is מְצַחֵק , and Sarah finds it worrying, so she tells Abraham to have him banished in order to protect Yitzchak, Issac.

ט וַתֵּרֶא שָׂרָה אֶת-בֶּן-הָגָר הַמִּצְרִית, אֲשֶׁר-יָלְדָה לְאַבְרָהָם--מְצַחֵק.
9 And Sarah saw the son of Hagar the Egyptian, whom she had borne unto Abraham, making sport.
י וַתֹּאמֶר, לְאַבְרָהָם, גָּרֵשׁ הָאָמָה הַזֹּאת, וְאֶת-בְּנָהּ: כִּי לֹא יִירַשׁ בֶּן-הָאָמָה הַזֹּאת, עִם-בְּנִי עִם-יִצְחָק.
10 Wherefore she said unto Abraham: 'Cast out this bondwoman and her son; for the son of this bondwoman shall not be heir with my son, even with Isaac.'

Most people translate it as "mocking" or "making sport."

Considering that we no longer use Hebrew the way it was used in the Bible, we have to take Biblical context to understand what things mean. Therefore I think that מְצַחֵק really means some sort of sexual activity.

Shavua Tov and Chodesh Tov