It means it’s a badly written pattern, that’s what it means.
But here is how I would interpret it. You are apparently making a slant outwards at the hip, so you are going to gradually increase.
So every 8th row, at the right edge, increase 1 st. Do this 5 times. This will take 40 rows and you will end up with 65 sts. Or, alternatively, it could mean that you are slanting INWARDS at the hip and so you need to DECREASE by 1 st at the end of each 8th row, 5 times, which would take 40 rows and leave you with 55 sts.
As for “thereby work acc co 1”, that has me totally stumped. Where did you get the pattern? If in a book or magazine, can you give the issue and page number? If it’s on-line, can you provide a link to the page?