generally, approximately
槪 centers on a broad, non-specific view: something general, approximate, or roughly outlined rather than precise.
槪 is the older form of 概. It combines 木 (tree/wood) with a phonetic component that likely contributed the sound ガイ. The right side historically relates to a measuring tool or leveling stick, giving the idea of a broad, approximate measure.
A wooden 木 ruler on the right side is used to level or smooth out details, giving only a rough, general outline rather than exact measurements.
For ガイ, imagine a guy giving a general, approximate answer while leaning on a wooden post: guy -> ガイ.