He spoiled his seed to no purpose (spoilage of seed)
Figuratively by metaphor: Onan.
("And Onan knew that the seed would not be with him, and it would be if he went in to his brother's wife and defiled the ground, to give seed to his brother" - Genesis 8:9)
Translation
Expression (Hebrew)
הִשְׁחִית זַרְעוֹ לְבַטָּלָה (הַשְׁחָתַת זֶרַע)
Definition (Hebrew)
בִּמְלִיצָה בְּהַשְׁאָלָה: אוֹנֵן.
("וַיֵּדַע אוֹנָן כִּי לֹּא לוֹ יִהְיֶה הַזָּרַע וְהָיָה אִם בָּא אֶל אֵשֶׁת אָחִיו וְשִׁחֵת אַרְצָה לְבִלְתִּי נְתָן זֶרַע לְאָחִיו"- בְּרֵאשִׁית לַח ט)