The story
The use of the word edgewise or edgeways (“with the edge facing in the direction of movement”) is metaphorical, suggesting that the gap or opportunity for a person to speak is very slim.
Etymology from Wiktionary, CC BY-SA 4.0.
get a word in edgewise
get a word in edge·wiseToday it means: To break into or participate in a conversation, especially where there is much interruption by other speakers. Full definition →