Consulting etymologies may help you recognize and remember meanings; but you must not regard etymologies as constitutive of meaning. That is the etymological fallacy:
The etymological fallacy is a genetic fallacy that holds, erroneously, that the present-day meaning of a word or phrase should necessarily be similar to its historical meaning. This is a linguistic misconception, and is sometimes used as a basis for linguistic prescription. An argument constitutes an etymological fallacy if it makes a claim about the present meaning of a word based exclusively on its etymology. This does not, however, show that etymology is irrelevant in any way, nor does it attempt to prove such.
A variant of the etymological fallacy involves looking for the "true" meaning of words by delving into their etymologies, or claiming that a word should be used in a particular way because it has a particular etymology.
The meanings of words extend and change over time, often in quite surprising ways. Etymology is of no value whatever in predicting meaning in any given instance, any more than, say, your own opinions can be deduced by investigating your father’s opinions.