Here are three sentences pulled semi-randomly off Google, all using the expression ‘by and large’.

• By and large they are a group of passionate cyclists who take pride in building some darn good mountain bikes!
• By and large they are looking for answers to the wrong question.
• By and large, life has been pretty sweet for the baby boomer generation.

The meaning is well-known to most English speakers —  on the whole, in general. The original meaning comes from the nautical world and describes two points of sail for a sailing vessel moving with respect to the wind. ‘Large’ refers to the wind coming from behind the boat, and so it would be pushing the boat forward. ‘By’ refers to the wind coming toward the front of the boat.  Early sailing ships could sail ‘by’ the wind, but only a few degrees above where the wind came straight across the side of the vessel. Modern sailboats with evolved sail shapes and rigging can sail ‘by’ the wind many more degrees above where the wind comes straight across the side of the vessel. They can ‘point’ much higher into the wind than the 17th-century square riggers. But, the early vessels could (and did) sail by the wind to the extent of their capabilities.  At that time, if a sailor described a boat as handling well ‘by and large’,  he was describing a sailing vessel’s performance under its two opposite endpoints of wind direction — not the general attribute  of simply ‘most of the time’ or ‘for the most part’.

The above examples illustrate how a word or phrase can shift its meaning over time from a concrete sense to an abstract one.  Here’s one more example for now. (There are many, many fascinating cases to look into.)

The verb ‘depend’ (rely on, require, need) has an archaic usage which is more concrete, it means to be physically attached to and dangling down from something, as in

• Silk tassels were depending from the lower circumference of the lamp shade.
• Their tongues depended from their mouths as they struggled up the hill in the heat of the tropical sun.

The current usage of ‘depend’ still implies a connection between things, but it is social or causal in an abstract way, not hanging by means of an immediate physical attachment.