Pardon = (formal) forgive; the act of excusing a mistake: ‘I’m sure they will pardon the occasional mistake.’

Excuse = give someone permission to stay away from school, work etc., or leave a classroom, meeting etc.: ‘Can I be excused from swimming today please?

I beg your pardon is used (1) to apologize to a stranger because you have bumped into them by accident, sat in their seat by mistake, etc.: ‘I beg your pardon. I didn’t know the table was reserved.’ (2) to politely ask someone to repeat what they have said: ‘Does this bus go to Marble Arch?’ ‘I beg your pardon?’ (3) when someone has said something that makes you feel surprised, shocked, angry etc.: ‘Who’s that woman with long hair?’ ‘I beg your pardon! That happens to be my wife.’

In formal situations, you can use excuse/forgive me instead of I’m sorry: ‘Please excuse me for taking so long to answer your letter.’

Painful = (1) causing physical or psychological pain: ‘The finger I trapped in the door is still very painful.’ ‘The child wriggled free and gave me a painful kick on the ankle.’ ‘His mischievous behavior brought back lot of painful memories.’(2) causing misery, pain or distress: ‘The painful process of treatment is going on.’ (3) exceptionally bad or displeasing: ‘This movie was painful to watch.’

Overdue= (1) (of payment) past due; being unpaid by the assigned date or at the scheduled time: ‘The electric bill was two months overdue.’ ‘An overdue installment’

Be/become overdue is used of payments, library books, video films that you have rented etc.: ‘Even if the books are only one day overdue, you still have to pay a fine.’

Expire is used of a license, contract, membership card, etc.: ‘I wanted to pay by visa, but my card has expired.’ ‘I suddenly realized that my driving license had expired.’

Outdoor (WITHOUT s) is an adjective. Outdoor = located, suited for, or taking place in the open air: ‘He enjoys the outdoor life.’ ‘There are many outdoor activities in and around Coimbra.’

Outdoors (WITH s) is an adverb. Outdoors = outside a building: ‘He likes to work outdoors.’

Outside = when you mean ‘away from’, use (get/go) out of (NOT outside): ‘It does you good to get out of the city now and again.’ ‘Without a passport, he would never have been able to get out of the country.’

In British English, outside is not used with of: ‘You aren’t allowed to park outside the bank.’

In American English, both outside and outside of are used.