Dear Sebastian, with 186 views at this point, we are all trying to help you, but I think it's your turn now to help us with more information, such as: where is this from; any flowers? Did you break open the fruit? Latex? Check your local flora!
... well then, it's what I thought initially, that it's something in MORACEAE ... so, Maclura was not so much off in the first place! ... so please check your local flora along those lines and let us know!
Could very well be ! Hydnocarpus is now in Achariaceae (with all the"cyanogenic" former Flacourtiaceae") ! But Mr. Pholtan said there was latex, and Achariaceae 's got none ! Maybe what was considered latex, was in reality "oil", which the seeds do have (e.g., chaulmoogra).