The status of this isogloss as a PWS feature is undermined by several circumstances(...):
(1) The autochthonous vs. borrowed status of Akk. ḫakāmu ‘to know, to understand’ has been hotly debated by several generations of Assyriologists and Semitists (v. Kogan 2011:111 for a select bibliography) (...)
(2) The Geez verb is attested only once in Pr 17:28. The semantic link between ‘se cohibere, continere’ (LLA 112) and “to be wise” is far from trivial, but fits well the sapiential context of “restraining one’s lips in order to look wise.” All other representatives of *ḥkm in EthS are borrowed from Arabic (Leslau 1990:341)
(3) Most of the meanings associated with this root in MSA are almost certainly due to Arabic influence. This is, however, much less evident as far as the meaning “to be old” is concerned: while also attested in Arabic (ḥakam- ‘a man advanced in age to the utmost degree,’ Lane 617), it seems to be too marginal there to be considered a reliable source of borrowing.
(4) As reasonably argued by A. Jeffery (1938:111), the genuinely Arabic meanings of ḥkm are “more in connection with the sense of govern,” whereas the meaning “to be wise” is likely due to Hebrew and Aramaic influence.
The meaning “to restrain, to withhold,” also rather prominently attested in Arabic, opens an interesting possibility of comparsion between PWS *ḥkm and Akk. ekēmu ‘to take away’.