Theoretical means existing in ideas and models rather than in tested practice. A theoretical model, theoretical physics, purely theoretical.
In science it names a branch rather than a criticism: theoretical physics is the work done with mathematics rather than apparatus, and it is not less real than experimental physics. In ordinary use, calling something theoretical means it has not been shown to work: a theoretical advantage. Note theoretically, which often carries the same doubt — theoretically it should work; and theory, which in science means a well-tested explanation, not a guess.
1adjectivetheoreticalExisting in ideas and models rather than in tested practice.
“The advantage is theoretical and nobody has measured it.”
2adjectiveworkingWorking with mathematics rather than experiment.
“She is a theoretical physicist and has never touched a telescope.”
theoretical is a quality of being in theory.
Greek theoretikos comes from theorein, to look at or contemplate — from theoros, a spectator. Theory, theatre and theorem all descend from the same act of looking, which is why a theory began as a way of seeing.
Latin
theōrēticus
Middle English
theorothycall
English, today
theoretical
From Middle English theorothycall, probably from Latin theōrēticus + -al, from Ancient Greek θεωρητικός.
Etymology from Wiktionary, CC BY-SA