The adjective 'episcopal' - pronounced with the stress on the second syllable i-PI-sker-perl, IPA: /ɛ ˈpɪsk ə pəl/ - means 'of, or relating to, a bishop', i.e., a senior member of the clergy of certain Christian denominations. Thus we may speak, e.g., of episcopal authority, i.e., the authority exercised by a bishop; a system of episcopal church government, i.e., a system in which bishops play a significant part in governing a church; or episcopal vestments, i.e., the ceremonial garments worn by bishops at religious services. The word 'episcopal', like the word 'bishop', comes from the Greek word ἑπίσκοπος (episkopos, 'overseer' or 'guardian').
Note that, while an episcopal church is any church which has bishops among its clergy, the Episcopal Church - 'Episcopal' spelt with an initial capital letter and preceded by the definite article - refers to the Anglican Church in Scotland or the United States.
There are two nouns related to 'episcopal':
'episcopate' - pronounced with the stress on the second syllable i-PI-sker-pit, IPA: /ɪ (or ɛ) ˈpɪsk ə pət/ - means either 'the position or status of a bishop' (e.g., 'Rowan Williams was elevated to the episcopate in 1991.') or 'the bishops of a church viewed collectively' (e.g., 'The episcopate has (or have) yet to make clear its (or their) views on this issue.')
'episcopacy' - pronounced with the stress on the second syllable i-PI-sker-per-si, IPA: /ɪ (or ɛ) ˈpɪsk ə pə sɪ/ - may mean either the same as 'episcopate' or 'the government of a church by bishops' (e.g., 'Many Protestant denominations have rejected episcopacy as a form of church government.')
As well as 'episcopal', there is the adjective 'episcopalian' (primazry stress on the fourth syllable, 'e-pis-ker-PALE-i-en' IPA: /ɪ (or ɛ) ˌpɪsk ə ˈpeɪ lɪ ən/, which may sometimes mean much the same as 'episcopal' but which also has the more specific meaning 'practising or recommending church government by bishops' - we might, e.g., describe someone as 'strongly episcopalian' if he or she strongly advocated church government by bishops. The word 'episcopalian' may also be used as a noun - someone who throughout his life had advocated church government by bishops might be described as 'a lifelong episcopalian'. It is probably better not to use the word 'episcopalian' unless you intend it in the second, more specific sense.
Note that when spelt with an initial capital letter 'Episcopalian' has a different meaning: it means 'of, or related to, the Episcopal Church' (see above). Similarly Episcopalian as a noun refers to a member of the Episcopal Church. So remember that not all episcopalians are Episcopalians.