Simple select query taking too long
You have almost 40000 rows where word='Facebook*'. I suppose that these rows are somewhat randomly scattered on the whole table. This means that Postgres has to read tens of thousands of random blocks from a disk, which might be slow.

You can try to cluster rows that have the same word together. You can use the command cluster misspelled using test_scanid;. This would take some time and block the table until done, so plan accordingly.