Critic David E. Wright Sr. points out that in the 1991 "uncut" edition of Stranger, the word grok "was used first without any explicit definition on page 22" and continued to be used without being explicitly defined until page 253 (emphasis in original). He notes that this first
Grok means "to understand," of course, but Dr. Mahmoud, who might be termed the leading Terran expert on Martians, explains that it also means, "to drink" and "a hundred other English words, words which we think of as antithetical concepts. 'Grok' means all of these. It means 'fear,' it means 'love,' it means 'hate'—proper hate, for by the Martian 'map' you cannot hate anything unless you grok it, understand it so thoroughly that you merge with it and it merges with you—then you can hate it. By hating yourself. But this implies that you love it, too, and cherish it and would not have it otherwise. Then you can hate—and (I think) Martian hate is an emotion so black that the nearest human equivalent could only be called mild distaste.
'Grok' means 'identically equal.' The human cliché 'This hurts me worse than it does you' has a distinctly Martian flavor. The Martian seems to know instinctively what we learned painfully from modern physics, that observer acts with observed through the process of observation. 'Grok' means to understand so thoroughly that the observer becomes a part of the observed—to merge, blend, intermarry, lose identity in group experience. It means almost everything that we mean by religion, philosophy, and science and it means as little to us as color does to a blind man."
The Martian Race had encountered the people of the fifth planet, grokked them completely, and had taken action; asteroid ruins were all that remained, save that the Martians continued to praise and cherish the people they had destroyed."
All that groks is God."