Structurally means 'as far as the structure goes' — looking at how a thing is built, or how its parts fit together, rather than at how it looks or feels. Builders use it most literally: a wall can be structurally sound (safe, holding up fine) or structurally unsound, and a crack can be ugly but structurally unimportant. From there it spreads. An essay can be structurally weak — the sentences are lovely, the order is a mess. Two languages can be structurally similar even when no words look alike. And it goes further still, into society: 'structurally unequal', 'structural racism' — the point of the word there is that the problem is in how the system is arranged, not in one bad person's choices, which is exactly why people reach for it in serious argument. A useful habit: whenever you see structurally, ask 'compared with what other way of looking?' — the word almost always sets the bones of a thing against its surface.