Full Idea
A sentence is generally a complex sign, so the thought expressed by it is complex too: in fact it is put together in such a way that parts of a thought correspond to parts of the sentence.
Gist of Idea
The parts of a thought map onto the parts of a sentence
Source
Gottlob Frege (Logic in Mathematics [1914], p.207)
Book Reference
Frege,Gottlob: 'Posthumous Writings', ed/tr. Hermes/Long/White etc [Blackwell 1979], p.207
A Reaction
This is the compositional view of propositions, as opposed to the holistic view.