The difference between Subsequently and Then

When used as adverbs, subsequently means following, afterwards in either time or place, whereas then means at that time.

Then is also noun with the meaning: that time.

Then is also adjective with the meaning: being so at that time.

check bellow for the other definitions of Subsequently and Then

Subsequently as an adverb:

Following, afterwards in either time or place.
Subsequently as an adverb:

Accordingly, therefore (implying a logical connection or deduction).

Then as an adverb (temporal location):

At that time.

Examples:

"He was happy then."
Then as an adverb (temporal location):

Soon afterward.

Examples:

"He fixed it, then left."

"Turn left, then right, then right again, then keep going until you reach the service station."
Then as an adverb (sequence):

Next in order; in addition.

Examples:

"There are three green ones, then a blue one."
Then as an adverb (conjunctive):

In that case.

Examples:

"If it’s locked, then we’ll need the key."

"Is it 12 o'clock already? Then it's time for me to leave."

"You don't like potatoes? What do you want me to cook, then?"
Then as an adverb (sequence):

At the same time; on the other hand.

Examples:

"That’s a nice shirt, but then, so is the other one."
Then as an adverb (UK, dialect, affirmation):

Used to contradict an assertion.

Then as a noun:

That time

Examples:

"It will be finished before then."