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στενός, στενή, στενόν narrow.

That is why shorthand is called 'narrow' writing (στενογραφία ) in quite a few languages.

τὰ στενά straits, mountain passes

So called because straits are very narrow. And so are mountain passes.

The old sailor said:
ἐμαχόμεθα rather than
ἐμαχεσάμεθα 
because he was thinking of that time spent fighting, rather than of the simple fact that, once upon a time, they fought the Persians there.

I'm sorry I can't do better on this picture. I simply can't work this photograph out at all. Where is north? Certainly not at the top of the picture as it is supposed to be unless stated otherwise.
They were sailing west, from Piraeus to Salamis, and from there south-est to Epidaur. The straits mentioned are between Salamis and Attica (capital: Athens), so we're looking either from the Piraeus towards Salamis, or from Salamis towards Attica. The "Battle at Salamis" was fought round the little island in the middle,